Is it possible to eat too much protein? In this post, we’ll summarize the research to see how much protein you need per day and what happens if you eat too much protein.
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Dietary protein is essential for life.
Protein deficiency, even when eating enough calories, leads to a condition known as kwashiorkor. Although rare in the developed world, this often occurs in areas during war, famine, and poor food quality. It is deadly if left untreated.
So there is a lower bound.
The USDA Guidelines recommend that at least 10% of your calories come from protein.
On a 2,000 calorie diet, 10% of your calories equates to roughly 50 grams of protein.
But can you eat too much protein?
If your diet is composed almost exclusively of protein, you may suffer from a condition known as protein-poising.
Protein poising is also known as rabbit starvation. Early trappers and settlers who subsisted on only rabbit meat (only around 8% fat), were recorded as suffering from systems of malnutrition that could lead to severe illness and death if not corrected.
So, there is an upper bound, too. Nearly 100% protein is also bad.
But how realistic is this warning?
Rabbit starvation is exceedingly rare. Can you think of any diets completely devoid of any fat or carbs?
Where, then, is a realistic, safe upper limit for protein intake?
Although the USDA Guidelines place an upper bound at 35% of your daily caloric intake (equating to roughly 175 grams of protein), there hasn’t been an upper limit established.
That is, there hasn’t been enough data to accurately established a consensus-based upper-limit before negative health effects begin.
Does that mean it’s safe to eat 35%? How about 36%? 50%?
As your body digests food, all proteins are catabolized into, among other things, urea.
Kidneys help filter things like urea out of the blood and into your urine for excretion. But in individuals whose kidney function is declining, urea can build-up in the bloodstream. Urea can be toxic as concentration increases and lead to poor health.
This may make sense for those with poor kidney health.
But what about healthy individuals with healthy kidneys?
Can they always filter out all urea?
Is there is a chance you can overload your kidneys with too much protein?
If you are eating too much protein from animal products - particularly red meat - you may be doing yourself some harm.
But this is primarily because of other nutrients like saturated fat that may be consumed in excess alongside these protein-dense foods.
What about _protein _itself?
A systematic review investigated the role of high protein intake near the upper end of the USDA Guidelines (greater than 20% of calories but less than 35% of calories) and markers of kidney health.
In healthy individuals, higher protein intake led to higher glomular filtration rate. This suggest your kidneys are working harder.
But was this necessarily a bad thing?
The review also found that high protein intake did not increase blood-based markers of poor kidney health. At least, not in the short term (6 months).
Another, older review of the literature came to similar conclusions.
It appears that high protein diets make your kidneys work harder. But it appears that’s okay.
Athletes who routinely consume 100% to over 200% of the recommended intake value of 0.8 grams of protein per kilogram of bodyweight also don’t show signs of kidney decline.
One big caveat with these studies is the length of time for which they were conducted.
Most studies were short-term (6 months or less).
Signs of kidney decline don’t seem to appear in the short-term, but does a high-work demand on your kidneys due to 5, 10, 20 years of a high-protein diet lead to poorer health?
Unfortunately, randomized control trials that last this long haven’t been done.
So, it appears high-protein diets don’t cause negative issues with your kidneys (or the development of kidney stones) in the short-term, but we simply don’t know how they affect kidney function over the long-term.
But are there other aspects of health besides kidneys that get affected by protein?
This is where the science gets interesting.
The science of aging is evolving rapidly.
How do chronic diseases develop?
How long do humans live?
Why do we even age at all?
What causes aging?
There are several questions we don’t yet have answers to. Most of the research on aging has been conducted on other animals.
Their findings, however, are intriguing and worth discussing. Some of them, interestingly enough, deal with eating too much protein.
A 2018 publication discusses some of the biochemical pathways associated with aging.
One popular mechanism that has been known to be associated with the aging process for decades is calorie restriction.
This is also what has led, in part, the rise in popularity of intermittent fasting. Similar biochemical pathways can be activated that have theoretical connections to a slower aging process.
Indeed, in many species (yeast, rats, even primates) calorie restriction leads to longer lifespans. Sometimes, markedly so.
But protein restriction is another area of research that shows signs of leading to an increased lifespan through similar biochemical pathways as calorie restriction.
It’s too early to tell if protein restriction leads to lower rates of chronic diseases or an increased lifespan. Much like calorie restriction, it is never safe to extrapolate all animal trials to humans. And it is difficult to run decades-long, longitudinal RCTs on humans.
So it may be a while before we really understand the nature of protein on longevity and where we can truly answer the question of “What is Too Much Protein?”
Healthy individuals likely won’t see any negative health effects from eating too much protein (even twice as much as the USDA Guidelines recommend at 0.8 grams of protein per kilogram of body weight).
Individuals with pre-existing renal disease may benefit from reducing protein intake.
Finally, some recent research suggests prolonged, protein restriction may lead to lower rates of disease and a longer lifespan. But the research is early, and it certainly isn’t definitive yet.
This is not intended to be medical advice. Please consult your doctor before making any major changes to your diet.
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